1. Field of the Invention
Embodiments of the present invention relates to an injection moulding machine, in particular an injection unit and a method for injection moulding plastic materials, in particular elastomers or caoutchouc material, according to cold channel and hot channel techniques.
2. Description of Related Art
Usually, according to the cold channel technique, several injection-moulded products are made simultaneously in one injection moulding process, wherein the caoutchouc material is led through a cold channel block in which individual channels extend to several cavities in a mould for the respective injection-moulded products. Before opening the mould, the injection piston of the injection moulding machine has to be retracted in order to relieve pressure from the cold channel, wherein the relatively long channels make the backflow of the material more difficult. Furthermore, known injection moulding machines are disadvantageous in that often waste material remains in the injection tube channel after the injection.
It is often the case with hot channel methods that the material remains at the wall of the injection tube channel and the machine nozzle in the form of a tube and the new material is passed through this tube. At high shear rate, the tube consisting of vulcanised material may come off and block the machine nozzle and the runner system. Thus, in order to ensure a complete emptying of the injection tube, in practice, a short “pre-ejection process” has to take place before.
DE 7 236 994 U1 discloses an injection moulding machine comprising a plastifying and injection unit having an injection cylinder and an injection piston positioned movably therein. The entire plastifying and injection unit is supported axially movably by means of the hydraulic cylinder. The injection piston is connected to two pistons arranged on both sides and supported in hydraulic cylinders of the injection cylinder in an axially movable manner. Moreover, the injection piston is formed as cylinder in which a plastifying screw is rotatably supported. The plastifying screw is, together with a motor, slightly axially movable relative to the injection piston via dynamic pressure cylinders in which pistons of the injection piston immerse.
DE 19 17 975 A1 discloses an injection moulding apparatus, wherein during plastification of the injection material introduced through a hopper into a plastifying cylinder, the screw is rotated by means of a motor via a gear. The discharge pressure thereby produced in the cylinder causes the screw to move axially rearwardly until it reaches its rear end position, in which the head of the screw is removed from the valve seat and consequently allows the plastified injection material the passing from the cylinder via the supply channel and a branch of the injection channel into the cavity of the cylinder which is increasing by simultaneous return of the piston. When the desired amount of injection material is in the cylinder, the injection process can be carried out.
DE 195 38 255 C2 relates to an injection moulding unit, wherein the piston feeds the plastified plastic material into an injection chamber while a piston provided in the injection chamber reverses.